In the field of wireless communications systems, i.e. radio systems, the use of relay transmitters is a well known way of enhancing the range of a “hop” or a link, i.e. a connection between a transmitter and one or more receivers. A relay transmitter, as opposed to a repeater station, is thus a transmitter which can pick up transmissions, demodulate and re-modulate them, and then retransmit them to the intended receiver in order to overcome geographical obstacles between the transmitter and the receiver.
In the case of encoded transmissions, for example so called FEC coding (Forward Error Correction), the relay transmitter decodes the transmissions in connection with the demodulation, and re-encodes them in connection with the re-modulation, and then retransmits the transmissions to the intended receiver.
In wireless communications systems, various types of retransmission schemes are often used in order to ensure that information from a transmitter reaches the receiver in a proper and intended fashion.
For single links, i.e. ones which do not use relay transmitters, there is a range of different principles for retransmission, such as for example, different kinds of ARQ (Automated Repeat Request), and HARQ (Hybrid ARQ).
When it comes to systems which use relay transmitters, or more properly relay “transceivers”, since the relay unit can both receive and transmit, the field of retransmission schemes for such systems is not as well explored as for systems which involve only a connection between a transmitter and a receiver.